C＃中PHP的number_format的等效功能是什么？

var upSize = 365308443361.28;
var downSize = 351897407979.52;

var size = upSize/downSize;

number_format(size, 3);

size.ToString(\"0.000\")

size.ToString(\"f3\")

var upSize = 365308443361.28;
var downSize = 351897407979.52;
var size = upSize / downSize;
string result = string.Format(\"{0:0.000}\", size);